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Using computer simulations, we study the isotropic-to-nematic nucleation in a fluid of colloidal hard rods as well as in a mixture of colloidal rods and non-adsorbing polymer. In order to follow the transformation of the system from the isotropic to the nematic phase, we use a new cluster criterion that enables us to distinguish the nematic clusters from the isotropic fluid phase. Applying this criterion in Monte Carlo simulations, we find two different regimes depending on the supersaturation. At low supersaturation we find nucleation and growth, while at higher supersaturation spinodal decomposition is observed. We determine the height of the nucleation barrier, and we study the structure as well as the shape of the nematic clusters. We discuss our simulation results in the light of classical nucleation theory.

We studied long-range repulsive glasses formed in suspensions of sterically stabilised charged colloidal poly(methyl methacrylate) particles (σ = 2.23 μm) with low polydispersity (4%) in the low-polar solvent cyclohexyl bromide (er = 7.92). Particle interactions were described by a long-range repulsive Yukawa potential. Glasses were obtained upon compression of the suspensions by centrifugation from a body-centred-cubic crystalline structure at low initial volume fraction (η ≈ 0.02) to a close-packed amorphous structure (η ≈ 0.64). Subsequent expansion of the sediment in gravity resulted in long-range repulsive glassy structures with volume fractions η = 0.16–0.64. The presence of small clusters (mostly dumbbells; clustered fraction fcl ≥ 0.12) formed by centrifugation prevented the glasses from crystallising for several weeks, while the sediment was still expanding. We used confocal microscopy to obtain three-dimensional datasets of the system and quantitatively analysed the structure of the glasses. The structure of the glasses was found to be remarkably similar to that of hard-sphere glasses, for which experimental data were obtained by centrifugal compression of silica spheres with a hard potential, despite the much longer-range interaction potential. After more than ten weeks the clustered fraction decreased due to spontaneous dissociation of the clusters, and finally bulk crystallisation of the glasses was observed into face-centred-cubic crystals with a volume fraction of around 0.22.

We perform Monte Carlo simulations to analyze the equilibrium dynamics and the long-time structural relaxation decay of columnar liquid crystals of disk-like colloidal particles. In the wake of recent studies on the columnar mesophase of hard calamitic (rod-like) colloids, we now focus on the diffusion of their discotic counterparts, here modeled as oblate hard spherocylinders. These systems exhibit a non- Gaussian column-to-column diffusion due to the combined action of transient cages and periodic freeenergy barriers. We find that at fixed packing fraction the barrier height increases with decreasing particle thickness, resulting into a more heterogeneous and non-Gaussian dynamics for thinner platelets, and reducing the inter-column diffusion coefficient. Moreover, we observe the characteristic two-step relaxation decay of the structure in the plane perpendicular to the column axis. By contrast, the in-column dynamics is similar to the typical single-file diffusion of one-dimensional dense fluids, with a relatively fast decay of the correlation functions.

Nucleation is an important stage in the growth of crystals. During this stage, the structure and orientation of a crystal are determined. However, short time- and length-scales make nucleation poorly understood. Micrometer-sized colloidal particles form an ideal model system to study nucleation due to more experimentally accessible time- and length-scales and the possibility to manipulate them individually. Here we report experiments and simulations on nucleation in the bulk of a hard-sphere fluid, initiated by seed structures configured using optical tweezers. We find that the defect topology of the critical nucleus determines the crystal morphology. From the growth of the crystals beyond the critical nucleus size, new insights into the role of defects in crystal growth were gained that are incompatible with the assumption of equilibrium growth. These results explain the complex crystal morphologies observed in experiments on hard spheres.